Switch from MySQL-python to PyMySQL
Switch from MySQL-python to PyMySQL

As part of the cross-project effort [1] to prepare OpenStack for
Python3 as the primary Python version used, the decision has been
made to switch from using MySQL-python to PyMySQL [2].

This patch switches Ironic to use the PyMySQL library.

[1] https://etherpad.openstack.org/p/liberty-cross-project-python3
[2] https://review.openstack.org/184388

Change-Id: I9c6906c37213a2a48c9aab3988b392fb7397ea90

juledwar/openstack-ansible-os_ironic,mrda/openstack-ansible-ironic,juledwar/openstack-ansible-os_ironic,mrda/openstack-ansible-ironic